BENDING MECHANICAL BEHAVIOR OF EPOXY MATRIX REINFORCED WITH MALVA FIBER

Transcription

1 BENDING MECHANICAL BEHAVIOR OF EPOXY MATRIX REINFORCED WITH MALVA FIBER Margem, J.I. (1) ; Gomes,V. A. (1) ; Margem, F. M. (1) ; Ribeiro, C.G. (1) ; Margem, M. R. (1) ; Monteiro, S. N. (2) (1) UENF - State University of the Northern Rio de Janeiro, Advanced Materials Laboratory, LAMAV; Av. Alberto Lamego, 2000, , Campos dos Goytacazes, Brazil, (2) IME- Military Institute of Engineering igormargem@gmail.com ABSTRACT Environmentally correct composites, made from natural fibers, are among the most investigated and applied today. In this paper, we investigate the mechanical behavior of epoxy matrix composites reinforced with continuous malva fiber, through bending tensile tests. Specimens containing 0, 10, 20 and 30% in volume of malva fiber were aligned along the entire length of a mold to create plates of these composites, those plates were cut following the ASTM standard to obtained bending tests specimens. The test was conducted in a Instron Machine and the fractured specimens were analyzed by SEM, the results showed the increase in the materials tensile properties with the increase of fiber amount. Keywords: epoxy composite, malva fiber, mechanical behavior, fracture analysis. 3528

2 INTRODUCTION Polymeric composites reinforced with natural lignocellulosic fibers, from different parts of plants, have been increasingly studied (1-3) and more and more industrially employed (4-6) by its technical and economical advantages. The engineering application of natural fibers extracted from cellulosecontaining vegetables, also recognized as lignocellulosic fibers, is presently considered an environmentally correct alternative to replace more expensive, non recyclable and energy-intensive synthetic fibers (7,8). In Brazil, the variety of natural fibers is an additional motivation for the research of new composites with those fibers (9,10), treated as green composites. In addition to environmental, economical and social benefits, some lignocellulosic fibers present specific properties that are comparable with synthetic ones used for polymer composite reinforcement. For instance, the specific strength (GPa.cm³/g) of curauá (1.31), sisal (0.92) and ramie (0.93) fibers, for very thin diameters (11), are relatively closer to that of glass fiber E (1.33). Therefore, it would be technically justified to replace glass fiber, which is more expensive, toxic and represents a problem to the environment (12), by a strong lignocellulosic fiber. However, some drawbacks such non-uniform dimensions and heterogeneous properties and incompatibility with a hydrophobic polymer matrix, reduce the potential of lignocellulosic fiber to be used as composite reinforcement (13,14). In particular, a low interfacial strength causes a weak adhesion between the hydrophilic fiber and the polymer matrix. Above the drawbacks natural fiber materials are being intensively studied as alternative to synthetics composite materials and the malva fibers can be used as reinforcement in composites polymer due to their relatively high strength and high impact resistance. Therefore, the aim of this work was to study the mechanical properties of the epoxy matrix composites reinforced with continuous and aligned malva fibers by bend tests. 3529

3 EXPERIMENTAL PROCEDURE The malva fibers investigated in this study were commercially supplied by Brazilian firm Castanhal Textil. Figure 1 illustrates a malva typical plant and malva fibers extracted from the stem. A B Figure 1. (A) Malva typical plant, (B) bundle of the Malva fibers as received The as received fibers of malva were cleaned and dried before use. The composites with 0, 10%, 20% and 30% in volume of aligned malva fibers were manufactured through accommodation of the fibers in a rectangular mold 152 x 122 x 10 mm and soaked with epoxy resin to complete the cavity, the procedure origins plates with were cut following the ASTM standard and the samples were three points bend tested in a model 5582 Instron machine with 100 kn of capacity at a strain rate of 1.6 x 10-2 s -1 and a span-to-depth ratio of 9. The fracture surface of the specimens was characterized after coverage with gold for scanning electron microscopy, SEM, Shimadzu microscope, Model SSX-550 operating at a voltage of 15 kv for the electron beam secondary. The flexural strength, f, were calculated by the following equation: (1) 3530

4 where F m is the maximum resistance force, L the distance between supports, and the extension associated with maximum force, the width b and d the thickness of the specimen. RESULTS AND DISCUSSION Figure 2 illustrates the typical appearance of load vs. elongation curves. The curves were recorded directly from the Instron machine, they revealed that malva fibers reinforced epoxy composites present limited plastic deformation. After a straight line, a sudden fracture occurs, indicating a brittle behavior for both pure epoxy an malva fiber composites tensile specimens. A B C D Figure 2. Load (N) versus Deformation (mm) curves, for malva/epoxy composites with different amount of malva fiber (A) 0%, (B) 10%, (C) 20% and (D) 30% in volume. The curves of Figure 2 was obtained the value of the maximum forces, F m, and the corresponding strain and was calculated by the equation 1 shown, flexural strength. Table 1 shows the average flexural strength resulting composite epoxy with different fractions of malva fiber. 3531

5 Table 1. Flexural strength and rupture displacement for the malva fiber composites. Amount of Malva Fiber (wt.%) Flexural Rupture Stress (MPa) ± ± ± ± 39.1 The graph for the flexural strength variation with the amount of fiber is shown in Figure 3. This graph implies that with the fiber volume increase the flexural stress increases too with a linear relation. So the results interpretation of the bending tests in Figure 3 indicate that the aligned fibers of malva constitute an effective reinforcement for over 10% composites with epoxy matrix. That is, as the fiber matrix is incorporated an increase in resistance occurs, which may be attributed a higher adhesion of the fibers by the resin. Figure 3. Variation of the flexural stress with the amount of malva fibers 3532

6 Figure 4 shows micrographs of typical fracture of composites with 30% of incorporation of the malva fiber in epoxy matrix, obtained by SEM. a) b) Figure 4 - SEM micrograph of composite obtained in 30% malva fiber reinforced epoxy resin (a) 50X and (b) 800X. In this figure, it can be noted, with smaller magnification (Figure 4a), the broken epoxy matrix with embedded fibers. With biggest increase (Figure 4b), it can be seen, pulling out evidences of fiber from the matrix. This seems to be a consequence of the weak adhesion between the fiber and the matrix so when exposed to the flexural stress the fiber slide a little bit and bakes when its not possible to slide anymore. CONCLUSIONS Epoxy matrix composites incorporated with continuous and aligned fibers of Malva fibers becomes more resistant to flexural for amount of fibers that exceeds 10% in volume. Up to 30% of Malva fiber volume fraction, the tensile strength increases around 55% in comparison to pure epoxy. SEM fractograph analysis revealed that the Malva fiber well adhered to the epoxy matrix served as an barrier to crack propagation. This justify the reinforcement effect. 3533

7 ACKNOWLEDGEMENTS The authors thank the support to this investigation by the Brazilian agencies: CNPq, CAPES and FAPERJ. REFERENCES 1. Bledzki, A.K and Gassan, J. Composites Reinforced With Cellulose- Based Fibers. Prog. Polym. Sci, 4 (1999) Nabi Saheb, D. and Jog, J.P. Natural fiber polymer composites: A review. Advances in Polymer Technology, v. 18, p , Eichhorn, S. J.; Baillie, C.A.; Zafeiropoulos, N.; Mwakambo, L.Y.; Ansell, M.P.; Dufresne, A. Review of current international research into cellulosic fibres and composites. J. Mater. Science, v. 36, p , Hill, S. Cars that grow on trees. New Scientists, v. 153(2067), p , Marsh, G. Next step for automotive materials. Mater. Today, v. 6(4), p.36-43, Zah, R.; Hischier, R.; Leão, A.L.; Brown, I. Curaua fibers in automobile industry A sustainability assessment. J. Cleaner Production, v. 15, p , Mohanty, A.K., Misra M. and Hinrichsen, G. Biofibers, biodegradable polymers and biocomposites: an overview, Macromolecular Mat. And Engineering, 276/277 (2000), Satyanarayana, K.G.; Wypych, F.; Guimarães, J.L.; Amico, C.S.; Sydenstricker, T.H.D.; Ramos, L.P. Studies on natural fibers of Brazil and green composites. Met. Mater. Proc., v. 17(3-4), p , Satyanarayana, K.G.; Guimarães, J.L.; Wypych, F. Studies on lignocellulosic fibers of Brazil. Part I: Source, production, morphology, properties and applications. Composites: Part A, v. 38, p , Monteiro, S. N.; Satyanarayana, K. G.; Lopes, F. P. D.; High strength natural fibers for improved polymer matrix composites, Materials Science Forum, (2010)

8 11. Wambua, P.; Ivens I.; Verpoest, I. Natural fibers: can they replace glass and fibre reinforced plastics?, Composites Science and Technology, 63 (2003) Crocker, J. Natural materials innovative natural composites. Materials Technology, 2-3 (2008) Monteiro, S.N.; Lopes, F.P.D.; Ferreira, A.S.; Nascimento, D.C.O. Natural fiber polymer matrix composites: cheaper, tougher and environmentally friendly, JOM, 61 (2009) Mohanty, A.K., Khan, M.A., Hinrichsen, G. Influence of Chemical Surface Modification on the Properties of Biodegradable Jute Fabrics-Polyester Amide Composites. Composites: Part A, v. 31, (2000) Mohanty, S., Verma, S.K., Nayak, S.K. Dynamic Mechanical and Thermal Properties of MAPE Treated Jute/HDPE Composites. Composites Science and Technology, v. 66, (2006)